Process for hardening protein fibre



Patented Oct. 7, 1947 curren STATES PATENT OFFICE PROCESS FOR HARDENINGPRoTEIN new Francis C larke Atwood, NewtongMassl assignor,

bymesfne assignments, toNational Dairy Broducts Corporation, New York,

tion of Delaware N. Y., a corpora- No Drawing, Application October29,1941, Serial No. 417,024

Claims. (01. ix-427.6)

used, such as the alkali-dispersible acid-coagulabl'e proteins derivedfrom cotton seeds, castor beans, natural wool, etc. All of such proteinsare dispersible in water with an alkaline material and can be formedinto fibre by spinning the dispersion into an acidic coagulating bath.All of these proteinsalso are hardened by formaldehyde and are thereforeadapted for treatment in accordance with this invention.

The complete process, in which my invention is an improvement, includesthe step of dispersing the protein with an alkaline material, preferablycaustic, but also including other inorganic alkaline materials, such asbases and alkaline salts, ammonia, organic bases, such as the variousamines, soaps and similar alkaline materials. This dispersion isaccomplished preferably by heating thetprotein and the alkaline materialin a suitable quantity of water to obtain a dispersion of highviscosity. After suitable filtering, centrifuging, cooling anddeaerating steps, the dispersion is forced through a spinnerette intoanacidic coagulating bath. The composition of thisbath preferably includessuch a portion of acid as to achieve a relatively low pH valuepreferably generally within the range of .75 to 2.5 and preferably abouta valueof 1.50. This bath may also contain a mineral and a vegetabletanning agent such as an alum and Goulac, respectively, and a solublesalt, such as sodium chloride or sulfate, or both, for dehydration. Thefibre is p plished in one or more baths containing an alkali metal saltof a strong, m ne-grand, such, as so-drum chloride orfsodiumfsulfate, ariiin'eral hardening agent such asalum, and formaldehyde in solution.The composition jofsuch 'a,'ba th or baths may Vary over relatively widelirnit s It is poss'ible, for example, to useiaplurality of. baths inwhich the first contains a relatively smaller proportion of formaldehydeor none fatall, and a higher proportion of salt, with for. withoutfanalum. such a. bath acts .pnmaniygas ahyiiertonic solution andca'usesdehydration or sh'rinkmg 'of the bre, butsome haras ing. action mayoccur depending on thefinclus'ion a damour p cr formaldehyde. A subseqlient bat 1 or'batlis'rnay include a much greater, concentration of vformale dehyde,..for example from .7 to 40%, preferably about to 20%..These baths may include asalt and also may incl'udef'a'n alum, ifdesired. The latter is no t so essentialat .thisflaterstag'e. -The saltis preferred in order to maintain the nit-e in a dehydrated condition.

The first bath is referred to as a pickling. particularly it doe s notcontain any formalde hyde or contains a small amount such as aconcentration of under, 5%., The second orsub se quent baths which containhigher concentrations of formaldehyde 'forexeifting a pronounced hardening action are referred to as hardening baths. One reason forusing twoba'ths instead, of one is occasioned by the fact that water eliminatedfrom the fibre which dilutes the bath, This is undesirable if. the bathis to contain a high percentage.oflformaldehyde. {It is preferable to have the dilution occur in the first bath, and to treat the, relatively,dehydratedfibre with more concentrated formaldehyde. ;l 3 ut asinglebath may be used if .the above disadvantage is of no commercialsignificance. A, a a V In all of these prior proposals, utilizing one ormore baths varying in composition asabove described and for the purposesabove mentioned, there has been no attempt insofar as; am aware, tocontrol the pl l value ofthe baths withina range which exerts a maximumhardening action. Particularly is this so inthe case ofthe bath or bathscontaining a relatively large concentration of formaldehyde in which theprimary hardening actionocc'urs. b L; J

It will be appreciated that the fibre being introduced into these bathsis in avery. acidic condition because itiis wet withthe coagulatingliquid, and eventhough an attempt is made tdiflein vs the acid whichgenera e thesurface of the fibre, the fibre is permeated with this acidand at a pH approximately that of the coagulating liquid. Sincerelatively large quantities of fibre are passed continuously throughthese baths, the baths take on the pH value of the fibre or at least arenot of such a composition as to alter appreciably the pH value of thefibre. Experience has shown that under actual manufacturing'conditionsthe pH value of the formaldehyde hardening bath will vary from 2.45 to3.17, depending upon the composition of the bath, the amountof fibrethat has been treated in the bath, etc. As far. as I am aware, noattempt has been made heretofore to alter the composition of these bathsexcept by varying the salt, alum and formaldehyde content.

Such variations do not result in pH values outside of the rangementioned above. While 'such baths. may have a pH value somewhat higherwhen ini tially fresh and before any fibre is introduced into H them,they very quickly fall to a pH value within Y the above range as .soonas the acid fibre is introduced into them.

I have discovered that a decidedly superior hardening action is obtainedif the pH value of the formaldehyde containing bath, such as the tity ofit renders it more easily controlled as to pH value. A bath whichcontains sufficient formaldehyde to exert an appreciable hardeningaction is much more difiicult to control as to pH value and has a morepronounced tendency to remain in an acid condition despite attempts toraise the pH value. This phenomenon may pos- 'sibiy be explained by theaction of the formaldehyde onthe protein. If it is assumed, as someauthorities say, that the formaldehyde acts primarily to block or reactwith the amino or alkaline groups in the casein or render them inactive,this wouldrender the casein itself more acidic which would tend tomaintain the bath in this condition. The maintenance of this pH valuemay be accomplished in a number of ways. For example, it is possible toadd alkaline material directly to the baths, but this has the dangerthat portions of the solution will have a pH value higher than theremainder of the bath with consequent nonuniformity of the fibre. tocirculate continuously the liquid of the baths through a treatingchamber to which appropriate amounts of caustic or carbonates may beadded so as to keep the pH value at the desired point. In a continuousoperation in which the bath is continuously full of fibre passingtherethrough,

it 'is not particularly convenient to use this method. This also has thedifliculty that such a control is very difficult since it'requiresconstant analysis, and within this pH range small amounts of caustic mayeffect an appreciable increase in pHvaluef V r N While any method maybeused for maintaining the pH value within the range above set forth, andpreferably at one point, within this range in order that the fibre beingprocessed may be uni form, I prefer to achieve this pH control by meansofa buffering salt in the treating'baths, particularly thebathcontaining'formaldehyde in a hardfactory results. To this solution isadded sodium It may also be possible 4 ening concentration. Thebuffering salt to be selected will depend somewhat upon the pH valueselected.

An alkaline material, such as caustic or soda ash, may be used to raisethe pH value to the desired amount, in combination with an appropriatebuffering salt to hold the solution at about the pH value achieved bythe addition of the al- .kaline material. a

An alkali metal acetate, such as sodium acetate, is very desirable whenthe pH range is to be maintained in the neighborhood of 4.5 to about 5.5or possibly 6.0 under certain circumstances.

In an embodiment of my process that is particularly practicalunderpresent day manufacturing conditions, the pickling solution may comprisean aqueous solution containing 3 to 15%,.

preferably 5 to 10% of a soluble salt, such as sodium sulfate or sodiumchloride, or both, formaldehyde in an amount 0 to 5%, preferably 1 to3%. and sodium acetate and alkaline materials i amounts to achieve andmaintain a pH value within the range of 4.5 to 5.2. Thehardening bathmay contain formaldehyde in an amount of 5 to 40%. limit are notrequired, however, for good results, and a range within 7 to 10% isdesirable for satisacetate and alkaline materials in such amounts as toachieve and maintain 'a pH value within the range of 4.5 to 5.2. Ifdesired other soluble salts, such as sodium chloride or sodium sulfateor both, may be included, but this is not so essential for a hardeningsolution, although desirable to maintain the fibre in a dehydratedcondition. Alum may also be added but is generally not necessary, V g rWhen utilizing a higher pH value, this is obtained by the use of, otherbuffering salts, as is well known in the art; for example, suitable proeportions of citric acid and di-sodium phosphate,

and also suitable proportions of mono-so'dium diacid phosphate anddi-sodium mono-acid phosand probably superior resultspas indicated hereparticularly if a rapid'reaction is de-j inafter, sired.

tained in accordance with my invention,'a fibre prepared in theconventional mannerby hardening it in an ordinary bath containing20%formaldehyde, 5% salt and 5% alum and having a pH value of 1.5, wascompared with a fibre hardened in a bath containing 20% formaldehyde andother ingredients similar buthaving the pH value of 6.5. The samplesoffibre treated in the two harsh and welded together, whereas inthehardwhereas the fibre formed in the bath with a higher pH value is more firmand of afib rous nature. These results were checked 'byfcomparing thefibre treated in bathssuch as mentioned above] Concentrations as high asthe upper As indicative of the results thatmay be obbut having pH valuesof 2.7 and 5.7, respectively. The results were quit similar.

As further illustrative, the following example is given with referenceto a bath containing a lower concentration of the formaldehyde. A bathcontaining 7% formaldehyde, 2 /2% salt, 2 /2% alum, and havin a pH valueof 3.45 was compared with a similar hardening bath containing the sameamount of formaldehyde but buffered to a pH value of 6.56. A comparisonof the fibres treated in these two baths shows that in the more acidicbath after one hour treatment, the fibre was brittle and weldedtogether, whereas after hardening in the bath of higher pH value fortwenty minutes, a fibre was obtained which was soft, not welded, andreadily carded. This indicates that much lower concentrations offormaldehyde may be used upon increasing the pH Value of theformaldehyde bath. In a commercial operation operating at a pH value of6.0, a formaldehyde concentration of 5% gives excellent results.

As a further example, a hardening bath containing 18% formaldehyde andwithout any salt or alum was adjusted to a pH value of 3.5; a fibre Itreated therein for one hour and dried resulted in a brittle weldedmass; a fibre treated in an identical bath but buffered to a pH value of6 was an excellent fibre in ever respect. This indicates that uponproper control of the pH value, the amount of salt or alum in thehardening bath may be greatly reduced if not entirely eliminated, andthe time of reaction may be greatly shortened.

I have also discovered that when utilizing formaldehyde baths in whichthe pH value is controlled as above noted, that superior results areobtained if the temperature is maintained within relatively criticallimits; and also a much more shorter treating operation is required.

While the desirable results in accordance withv my invention may beobtained utilizing a bath at room temperature, providing the treatmentis prolonged somewhat, I have ascertained that the maximum speed inhardening and the greatest superiority in the fibre is obtained if atemperature range of from 100 to 125 F., preferably 115 to 120 F.'ismaintained in the formaldehyde hardening bath. Investigations indicatethat a bath containing 5% formaldehyde buffered to a pH value of 6.0 or6.5 and at a temperature of 115 to 120 F. gives a satisfactory hardenedfibre in 10 to 30 minutes. This is to be compared with the prior artknown requirements of from 10 to 12 hours.

I have also discovered that when utilizing a formaldehyde bathmaintained at the above pH value and preferably within preferabletemperature ranges, that desirable results are obtained with respect tostrength and fibre diameter if the fibre is kept at constant lengthwhile in the bath or baths so that it is not permitted to shrink,particularly in the case of the hardening bath. This action is referredto more generally as tensioning. While the fibre may actually beelongated during this treatment, it is practical that the fibre, whilein the hardening bath, may be suspended between rollers or run in loopsbetween rollers or other suitable means whereby it is maintained at thesame length during the treatment in the bath and thus preventingshrinkage. As further illustrative of this aspect of my invention, afibre which is introduced into an ordinary hardening bath at the rate of220 feet'p'er minute and permitted to stand in the bath for one hourwithout being subjected to any tension, would be withdrawn from the bathat the rate of. to feet per minute. This indicates the shrinkage inlength of the fibre that takes place during the hardening. If the fibre,while it is in the hardening bath, is maintained at constant length,such as passing it continuously between rollers so as to be in loops offixed lengths, whereby the continuous strand entering and leaving thehardening bath moves at the same rate, it has been found that the fibreis greatly improved in strength and is of a much smaller desirablediameter. The results are indicated in the following table:

Tension Strength in During Pounds per Hardening Square Inch DiameterFro-m the above it will be seen that an increase in strength from 15 to50% is obtained and a reduction in fibre diameter of about 25%.

Throughout this specification I have indicated what I believe to be theupper and lower critical limits of the various factors when such limitsare critical for securing the new results in accordance with myinvention. I have also included a more limited range which I regard asthe optimum conditions either from the commercial standpoint or forsecuring the most favorable results. The inclusion of a statement of theoptimum conditions in order that 'my invention maybe practiced with thegreatest benefit and advantage is not intended to be inconsistent withthe critical nature of the range over which the new result may beobtained.

Fiber made in accordance with the invention is admirably suited fortreatment in subsequent processes such as acylating with ketene oracetic anhydride, deaminizing by nitrous acid, etc.

' It will be obvious that many variations may be made within myinvention as outlined above and that various expedients apparent tothose skilled in the art may be resorted to for carrying'into effect theinvention as described herein. I intend all such equivalents andvariations to be included within the scope of my invention.

This application is 'a continuation-in-part of application Serial No.309,028, filed December 13, 1939, now Patent No. 2,342,994.

Iclaim:

1. In a process of hardening a proteinaceous fibre that ha been formedfrom an alkali-dispersible acid-coagulable protein by dispersing saidprotein with an alkaline material and spinning the dispersion into anacidic coagulating bath whereby the fibre is impregnated with the acidin said bath, following which the fibre is stretched; the steps whichcomprise placing said acid coagulated and stretched fibre in a hardeningbath containing formaldehyde, and maintaining the pH value of said bathat not less than 4.5 and not more than '7 .0 during which time the fibreis hardened in said bath.

2. In a process of hardening a proteinaceous fibre that has been formedfrom an alkali-dispersible acid-coagulable protein by dispersing saidprotein with an alkaline material, spinning the dispersion into anacidic coagulating bath, and stretching the coagulated fibre; the stepwhich comprises hardening said coagulated and stretched fibre in aformaldehyde hardening bath maintained at a temperature of 100 to 125 F;

and at a pH value of not less than 4.5 and not over 7.0. V r A -3. Inaprocess of hardening a proteinaceous fibre'that has been formed from analkali-dispersible acid-coagulable protein by dispersing said proteinwith an alkaline material, spinning the dispersion into an acidiccoagulating'bath, and stretching the coagulated fibre; the step whichcomprises hardening said coagulated and stretched fibre while maintainedagainst shrinkage in a formaldehyde hardening bathhaving a temperatureof 100 to 125 F. and a pH value of not less than 4.5 and not over 7.0.

4.'In a process of hardening a'proteinaceous fibre that has been formedfrom an alkali-dis! persible acid-coagulable protein by dispersing saidprotein with an alkaline material, spinning the dispersion into anacidic coagulating bath, and stretching the coagulated fibre; the stepwhich comprises hardenin said coagulated and stretched fibre in ahardening bath containing formaldehyde in a concentration of at leastand buffered at a pH value of not less than 4.5 and not over 7.0 by abuffering salt. I

5. In a process of hardening a proteinaceous fibre that has been formedfrom an alkali-disand stretching the'coagulated fibres; the steps whichcomprise introducing said coagulated and stretched fibre into a firststage hardening bath containing not more than 5% formaldehyde, and 3to'15% of an alkali metal salt of a strongmineral acid and'buffered toapH value of not less than'4.5 and not over 7.0 by a buffering saltjandtransferring the preliminarily hardened fibre to a second stagehardening bath containing at least 5% formaldehyde and buffered to apH-value of not less than'4.5 and not over 7.0 by a buffering salt. I10; In a'process of hardening a proteinaceous fibrethat has, been formedfrom an alkali-dis- V persible acid-coagulable protein by dispersingsaid protein with an alkaline material, spinning the dispersion into anacidic coagulating bath, and stretching the coagulated fibre; thestepswhich comprise introducing said coagulated and persible acid-coagulableprotein by dispersing said protein with an alkaline material, spinningthe dispersion into anacidic coagulating bath, and stretchin thecoagulated fibre; the step which comprises hardening said coagulated andstretched fibre in a hardening bathcontaining formaldehyde in aconcentration of at least 5% and maintained at a pH value of not lessthan 4.5 and not over 7.0 by the buffering action of sodium acetateincluded in said bath.

6. In a process of hardening a proteinaceous fibre that has been formedfrom an alkali-dispersible acid-coagulable protein by dispersing saidprotein With an alkaline material, spinning the dispersion into anacidic coagulating bath, and stretching the coa'gulatedfibre; the stepwhich comprises hardening said coagulated. and.

stretched fibre in a hardening; bath containing formaldehyde in aconcentration of at least 5% and maintained at a temperature of 100120125 F., and a pH value of not less than 4.5 and not an alkalinematerial, spinning the dispersion into an acidic coagulating bath, andstretching; the coagulated fibre the step which comprises hardening saidfibre while maintaineclragainst shrinkage in a hardening bath containingformaldehyde in a concentration of at least 5% and maintained ata'temperature of 100 to 125 F;, and a'pHvalue of not less than 4.5 andnot over 7 .0 by the buffering action of sodium acetateincluded in saidbath.

8. In a process of hardening 'a proteinaceous fibre that has been formedfrom analkali-dise persible acid-coagulable protein by dispersing saidprotein with an alkaline material, spinning.

I containing not more than 5% formaldehyde, and

3 to 151% of an alkali metal salt of a strong mineral acid, and having apH value of not less than 14,5 and not over 7 .0; and transferring theprelim inarily hardened fibre to" asecond stagehardeni-ng bathcontaining atleast 5% formaldehyde stretchedfibre into a first stagehardening bath containing not more than 5% formaldehyde, and

3 to 15% of an alkali metal salt of a strong min and-a pH value of notless than 45 and not over 11. In a process of hardening a casein fibrethat has been formed by dispersing said casein with an alkalinematerial, spinning the dispersion into an acidic coagulating bath, andstretching the coagulated fibre; the steps which comprise introducingsaid coagulated and stretched fibre into a first stage hardeningbath'containing not more than 5% formaldehyde, and 3 .to.15% of analkalimetal salt of a strong mineral acid; and hav-- V in apH value'of.not less than 4.5- and not'over. 7.0 and transferring the preliminarilyhar dened fibre to second stage hardening bath con tainingjat least 5%formaldehyde and buffered to a pH value of notless than 4.5 and not over7.0 by means of sodium acetate.

12. In aprocess of hardening a casein fibre that hasfbeen formed bydispersing said casein with an alkaline material, spinning thedispersion, into an' acidic coagulating bath," and stretching r thecoagulated fibrej the steps which comprise introducing said coagulatedand stretched fibre into a first stage" hardening bathrcontainingnotmore'than 5% formaldehyde, 3 to 15% of sodium chloride,:anol buffered toa pHvalue of not: less than 4L5and not over 7.0 by'sodium acetate, andtransferring the preliminarily hardened fibre to a secondstage hardeningbath containing at least 5% formaldehydeand maintained at a temperatureof 10o to fF. and buffered to apH value of not less than 4.5 andnot.over7.0 by means.

of sodium acetate; v

13. In a process of hardeninga has been formed by dispersing said;'casein with an alkaline material and continuously spinning thedispersion into an acidic coagulating bath 7 whereby the fibreisimpregnatediwith the acid in 5 said. bath, following whichthe'coagulated fibre 'l isstretched; the steps whichcomprise continu-.ously introducing said: acid coagulated iand stretched fibre into afirst stage hardening bath containing not more than formaldehyde, 3 to15% sodium chloride and buffered to a pH value of 4.5 to 5.2 by theinclusion of sodium acetate in said pickling bath and the neutralizationof any acid introduced with the fibre into said bath, permitting thefibre to remain in said bath for from 10 to 60 minutes, continuouslyremoving the fibre from said bath and transferring the preliminarilyhardened fibre to a second stage hardening bath containing at least 5%formaldehyde, 5 to sodium chloride, and maintained at a temperature of110 to 125 F. and buifered to a pH value of 4.5 to 5.2 by means ofsodium acetate.

14. In a process of hardening a proteinaceous fibre that has been formedfrom an alkali-dispersible acid-coagulable protein by dispersing saidprotein with an alkaline material and spinning the dispersion into anacidic coagulating bath whereby the fibre is impregnated with the acidin said bath, following which the coagulated fibre is stretched; thesteps which comprise continuously introducing said acid coagulated andstretched fibre into a hardening bath containing formaldehyde and analklai metal salt of a strong acid, and maintaining the pH value of saidlastmentioned bath at not less than 4.5 and not over 7.0 by neutralizingany acid introduced into said bath by said fibre and by incorporating insaid bath an alkali metal salt of a weak acid.

15. In a process of hardening a proteinaceous fibre that has been formedfrom an alkali-dispersible acid-coagulable protein by dispersing saidprotein with an alkaline material and spinning the dispersion into anacidic coagulating bath whereby the fibre is impregnated with the acidin said bath, following which the coagulated fibre is stretched; thesteps which comprise continuously introducing said acid coagulated andstretched fibre into a first stage hardening bath containing a smallamount of formaldehyde and alkali metal salt of a strong mineral acid,maintaining the pI-I value of said bath at not less than 4.5 and notover 7.0 by incorporating therein buffering salt and by neutralizing anyacid introduced into said bath by said acid coagulated fibre;continuously transferring the fibre to a second stage hardening bathcontaining at least 5% formaldehyde and an alkali metal salt of a weakacid to maintain said bath buifered to a pH value of not less than 4.5and not over 7.0.

FRANCIS CLARKE ATWOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Brother and McKinney, ProteinPlastics From Soybean Products from Ind. and Eng. Chem, Nov. 1938, pgs.1236-40.

La processus de durcissement dans ldustrie de la galalithe J.DelormeRev. Gen. Mat. Plastiques, 1936, T. 12, No. 3, pgs. 74-76, Mars.from Chemie and Industrie, Cas. Dig.

Mougeot, Formaldehyde in the Hardening of Casein Objects from Rev. Gen.des Matieres Plastiques, Feb. 1928, vol. 14, No. 2, pages 35-37.

Certificate of Correction Patent No. 2,428,603. October 7, 1947.

FRANCIS CLARKE ATWOOD It is hereby certified that errors appear in theprinted specification of the above numbered patent requiring correctionas follows: Column 7, line 56, claim 7, after the word said insertcoagulated and stretched; column 8, line 48, claim 11, for "to secondread to a second; column 9, line 25, claim 14, for alklai read alkali;column 9, line 15, beginning with In a process strike out all to andincluding the Word and period acid. in line 30, comprising claim 14, andinsert the same after claim 1, as claim 2; same column, line 31,beginning with In a process strike out all to and including the numeraland period 7.0. in column 10, line 9, comprising claim 15, and insertthe same after claim 8, as claim 10; and for the claim numbers 2, 3, 4,5, 6, "7", 8, 9, 10, 11, '12, and 13, read 3, 4, 5,6, 7', 8, 9, 11, 12,13, 14, and 15, respectively; and that the said Letters Patent should beread with these corrections therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 27th day of January, A. D. 1948.

THOMAS F. MURPHY,

Auistant oommiasiogwr of Patenta.

